...the 9mm AR or the 223 AR?  
Doesn't the rotating bolt of the 223 absorb more recoil, yet the blowback operation of the 9mm transfers it all to the shooter?

What do you think? Can you tell a difference between the two?

Its hard for me to tell the difference. Maybe I need to take both out to the range at the same time.

.223

Of my four ...

the Oly 10mm has by FAR the most recoil due to the blowback design...

Next comes the 16" .223 lightweight w/ fluted barrel and Ace stock... followed closely by my very stock 20" hbar...

and finally, my 6mm PPC with 24" stainless bull and 6-18x50mm scope weighs a ton and has very close to no recoil.

Scot  

IMO , 5.56mm recoil is nearly identical with 9MM recoil.

9mm.

It is direct blowback, and the bolt is heavier, which you do feel when it comes hurling rearward.

You could try to decrease recoil by adding a shorter spring inside the standard spring to make the "jolt" against the back of the buffer tube less but I doubt that is what you were asking.  Remember, AR15 was designed for 5.56 and adapted to 9mm which means that it isn't the most ideal system although it is still very good.

Basically your peak force is probably going to be higher with 9mm, given similar bolt/carrier speeds but higher bolt mass with 9mm and the same stopping speed with both.

Just what I think...

I thought it was just me. I took my colt w/the collaspible stock to the range to sight in an Aimpoint. I had it on a bench, so the stock was exactly in the same place on my shoulder each time. I could not believe how much the recoil started to bother me, it was uncomfortable after awhile. Maybe I'm just soft, but I'm thinking the answer is 9mm has more recoil.